N-phenyl-p-phenylenediamine as antiozonant for butadiene-styrene rubbery copolymer



United States Patent N-PHENYL-p-PI-IENYLENEDIAMINE AS ANTI- OZONANT FOR BUTADIENE -STYRENE RUBBERY COPOLYMER Joseph C. Ambelang, Akron, Ohio, assignor to The Firestone Tire & Rubber Company, Akron, Ohio, a corporation of Ohio No Drawing. Application December 16, 1955 Serial No. 553,442

2 Claims. (Cl. 260-453) This invention relates to the use of monoraryl-substituted paraphenylenediamines (p-aminodiphenylamines) as antiozonants in the rubber copolymer of butadiene and styrene, known as GR-S. The invention includes the stabilized rubber and its vulcanization.

The phenyl groups of the p-aminodiphenylamines may be unsubstituted, or either or both of the phenyl groups may be substituted. Likewise, either or both of the amino groups may be substituted. The antiozonants may contain one or more substituents, and there may be substituents in both one or both of the phenyl groups and one or both of the amino groups. The possible substituents are alkyl or other aliphatic hydrocarbon groups of 1 to 8 carbon atoms, and one or both aryl groups may be chlorine substituted.

Thus the antiozonants of this invention may be represented by the following formula where the amino groups are para to each other, where R is from .the. class .consisting of unsubstituted aryl groups, chlorine-substituted aryl groups, and aryl groups substituted with aliphatic hydrocarbon groups containing 1 to 8 carbon atoms, including aryl groups in which there is more than one substituent, and where R is from the class consisting of hydrogen and aliphatic hydrocarbon groups containing 1to'8 carbon vatomst,.. 'l.,h,us, the antiozonants include in addition to N-phenyl-p-phenylenediamine, substituted N-phenyl-p-phenylenediamines including, for example, the following: 1

N- 4-tt-octylphenyl) -p-phenylenediamine N-(4-ethylphenyl)-p-phenylenediamine N- 3 ,4-dimethylphenyl) -p-phenylenediamine N-(4-ethylphenyl)-p-phenylcnediamine N- 2,3,5 -trimethylphenyl -p-phenylenediamine N-(4-butylphenyl) -p-phenylenediamine N- 4-ethylphenyl) -p-phenylenediamine -N- 4-amylphenyl) -p -phenylenediamine N- 4-octylphenyl) -p-phenylenediamine N- 4-chlorophenyl) -p-phenylenediamine N- (-4-cyclohexylphenyl) -p -phenylenedi amine N- beta-naphthyl -p-phenylenediamin e -ber 1951).-

2,905,654 Patented Sept. 22, 1959 Oxygen and ozone both have a harmful elfect on rubber, but the efiect of each is diflerent, and compounds which inhibit or prevent the harmful effect of one are not necessarily effective in stopping or retarding the harmful efiect of the other.

Crabtree and Kemp in an article in Industrial and Engineering Chemistry, vol. 38, starting at page 278 (1946), explain the difference in the action of oxygen and ozone on rubber. The light-catalyzed oxidation which occurs during outdoor exposure forms a skin and crazed appearance over the exposed surface of the rubber. Ozone, on the other hand, even in very low concentration, induces cracking in rubber, but only if the rubber is stretched (C. H. Leigh-Dugmore, Rubber Age and Synthetics (London), November 1952, pages 398, 399 and December 1952, pages 442, 444, 445.) The cracks are perpendicular to the direction of stretch. Such cracking can occur in the absence of light. Compounds which inhibit ozone deterioration are referred to herein as antiozonants.

Tires are stressed when inflated. While a tire is at rest it is stretched statically, and on a moving vehicle it is stretched dynamically, i.e., it undergoes alternating stretching and relaxing. Some of the antiozonants are more effective in static tests and others are more effective in dynamic tests. Antiozonants which are effective under both conditions will be desired for tires, but for other rubber products an antiozonant which does not meet both .tests may be used.

The inhibiting effect of the antiozonants of this invention on rubber was determined by treatment of unaged, cured stocks with air of controlled ozone content in specially designed equipment. The tests were conducted with one-half inch dumbbell samples of approximately 100 gauge thickness. The special apparatus for testing with air of controlled ozone content, and the method of testing therein are described in the articles by Ford and Cooper, entitled A Study of the Factors Affecting the Weathering of Rubber-like Materials, I and II, appearing in India Rubber World, vol. 124, pages 696698, 701 (September 1951), and vol. 125, pages 55-60 (Octo- The following reports refer to tests in some of which the ozone concentration was maintained at 25 parts per 100,000,000 and in one of which the ozone concentration was maintained at parts per 100,000,000. Two types of tests were conducted. In one type, called the dynamic test, the sample was repeatedly stretched between the limits of 0 and 20 percent elongation at the rate of 108 cycles per minute. In the other type of test, the static test, the samples were stretched at 12.5 percent elongation throughout the test. On completion of each test the number and size of the cracks in each sample were compared visually with the number and size of the cracksin a blank strip from the same masterbatch which contained no antiozonant and which was cured and tested at the same time as the test sample. The number of cracks was reported on an arbitrary scale as follows: none, very few (or v. few), few, moderate, moderate-to-numerous (or mod.-num.), and numerous. The size of the cracks was reported according to an arbitrary scale as follows: very slight, slight, moderately severe (or mod. severe), severe, and very severe.

In all of the reported tests 2.0 parts by weight of an antiozonant were added to the control formula or masterbatch for each 100 parts of rubber present. The reported results include data on the tensile properties of the cured rubber stocks before and after aging under the conditions stated with respect to the various examples. The modulus and tensile strength are given in pounds per square inch, and the elongation is reported as percent of stretch at the break. These data are included to show that the antiozonants have no substantial deleterious effect upon the cure or upon the aging of the cured stocks.

The rubber may be vulcanized with sulfur or a sulfur donor or with a cross-linking agent such as a dithiol, nitroor nitroso-compound, etc. Known vulcanization accelerators are useful in speeding up the vulcanization process and operative herein, especially the relatively active accelerators of sulfur vulcanization, including the thiazole sulfenamides, e.g., N-cyclohexyl-Z-benzothiazolesulfenamide, thiazoline sulfenamides, thiocarbamyl sulfenamides, mercaptothiazoles, mercaptothiazolines, thiazolyl monoand (ii-sulfides, the N,N-disubstituted dithiocarbamates, the thiuram sulfides, the xanthogen sulfides, and metallic salts or mercaptothiazoles or mercaptothiazolines or dithiocarbamic acids.

One or more accelerator activators are often used with any of the accelerators mentioned, and such activators include the various derivatives of guanidine known in the rubber art, amine salts of inorganic and organic acids, various amines themselves, and alkaline salts such as sodium acetate and the like, as well as other activators known in the art. Additionally, two or more accelerators or accelerator combinations are sometimes desirable in a single rubber compound. Many of the accelerators mentioned above are suitable in latex formulations, especially such common accelerators as piperidinium pentamethylene dithiocarbamate, zinc butylxanthate, zinc ethylzanthate, zinc salt of mercaptobenzothiazole, zinc dimethyldithiocarbamate, and zinc dibutyldithiocarbamate. Although vulcanization is usually accomplished by heating a vulcanizable rubber composition at a temperature in the range of 240 to 400 F. for a time ranging from several hours to a few seconds, vulcanization does take place at lower temperatures such as ordinary room temperature. It is quite common to vulcanize a latex film containing an ultra-accelerator by allowing the film to remain at room temperature for several hours or a few days.

Various tests were made on the use of N-aryl-substituted p-phenylenediamines. The first tablegives the physical properties, before and after oven-aging four days at 212 F., as well as data on the effect of ozone on a cured tread stock. The antiozonant was added to the following masterbatch made from rubber copolymer of hntadiene and styrene known as GR-S;

.Parts by weight GR-S 100 Sulfur 1.7

Black 45 Stearic acid 2.5 Zine oxide 2.4 Accelerator 1.2 Softener 6.6

Total 1552;4-

Thesamp les were amass minutes at 280'" F.

Table I.-T read stock Blank Test Masterhatch 159.4 169.4 N-phenyl-p-phenylenediamine 2 Total 159. 4 161. 4

Physical properties:

Before aging- 300% modulus 875. Tensile strength.-. 3,675. Elongation 640.

After aglng- 300% modulus 1, 650.

Tensile strength 2, 000.

Elongation 340. Ozone cracking (7 hrs. at 60 p.p.h.m. at F S atic- Frequency Numerous V. few. Size Mod. severe. Slight.

Frequency Numerous None. Size Slight 1 Test strips for physical properties were lost.

The antiozonant had no bad effect on the curing of the rubber, and was quite satisfactory as an antiozonant as judged by the reduced frequency and size of the cracks produced in the stock containing it. In' the dynamic test the antiozonant eliminated cracking under the test conditions.

A further test was made by compounding further N- phenyl-p-phenylenediamine with the same tread stock masterbatch. The stocks were aged only 2 days at 212 F. The results are recorded here.

Table 11.Tread stock Blank Test Masterbatch 159. 4 159. 4 N phenyl-p-phenylenedlamine 2 Total.- 159.4 161.4

Physical properties: Before aging- 300% modulus. Tensile stre Elongation 555 6 After aging- 300%modulus 2,090 1,750. Tensile str 2,400. 2,450. Elongation 320 390. Ozone cracking (7 hrs., room temp., 26

p.p.h.m.): Statio- Frequeney Moderate-.. V. few. Size Mod.severe. Slight. y

V numer- Moderous. ate. Slight--..... V. slight.

The antiozonant was quite .eifective in reducing the attack of ozone, and had no noticeable bad influence on the vulcanization or vulcanizate.

Tests were made on sidewall stock prepared from a As wax has been found beneficial in its effect, was included in ne of the test stocks as indicated in the followi g table in whicn theresults. are The stocks were cured 60 minutes at 280 F. They were aged 4 days at 212 F. The results are recorded below:

Table lII.Sidewall stock bon black and a small amount of N-phenyl-p-phenylenediamine as an antiozonant.

Blank Test Blank Test +wax +wax Masterbatch 161. 3 161. 3 161. 3 161. 3 N-phenyI-p-phenylenediamine 2. 2. Wax- 3. 3.

Total 161.3 163.3 164.3 166.3 Physical properties: Before aging- 300%modu1us 1,575 1,450.-.. 1,400 1,250. Tensile strength 2,300 170..-. 2,075 1,850. Elnnrmtinn 410 430 420 After aging- Tensile strength 1,975 1,975..-. 1,610 1,750. Elongation 200 40 200 240. Ozone cracking (7 hrs. at room temp, 25

p.p.h.r n.): Stanc- Frequency Few V. Few. None. None.

'2 Mod. sev Slig Dynamlc Frequency Numerous None. Size Mod. sev.

The presence of N-phenyl-p-pheny1enediamine in the 25 References Cited in the file of this patent test stock is seen to have reduced the severity and size UNITED STATES PATENTS of the ozone cracks under statlc conditlons. In the 1950 478 C 1 presence of both wax and N-phenyl-p-phenylenediamine 2377423 i 1934 no ozone cracking occurred during conditions of the 2379936 ow an at June 1945 test while in the presence of wax alone numerous severe 3O 2'419736 gi July cracks were formed under dynamic conditions. oan APL 194 The examples and test results are illustrative. The in- FOREIGN PATENTS vention is covered by the claims.

Whatl claim is: 23,533 Austraha July 17, 1935 1. Sulfur-vulcanized rubber copolymer of butadiene 35 and styrene containing carbon black and a small amount of N-phenyl-p-phenylenediamine as an antiozonant.

2. The process of producing vulcanized rubber copolymer of butadiene and styrene, which process comprises sulfur-vulcanizing the copolymer containing car- OTHER REFERENCES Shaw et a1.: Antiozidants for GR-S Rubber, Rubber World, August 1954, p. 636-642. 

1. SULFUR-VULCANIZED RUBBER COPOLYMER OF BUTADIENE AND STYRENE CONTAINIGN CARBON BLACK AND A SMALL AMOUNT OF N-PHENYL-P-PHENYLENEDIAMENE AS AN ANTIOZONANT. 